This invention relates generally to strain testing and more specifically to high level, biaxial strain testing of aerospace structural materials such as aluminum, titanium, boron-aluminum composites and the like, where long gage life and miniature size are desired.
The measurement of strain in the testing of materials, especially fatigue testing, requires gages that will measure high strain levels over many load cycles. The availability of a gage having such characteristics is further restricted where biaxial strain measurement is desired, and/or the principal strain axes are generally unknown and/or the surface area available for gage placement is restricted. Short gage length resistance type metal foil strain gages have been used in some applications but the considerable time and effort required for attachment and the inability to reuse the gages at other locations generally make them unsatisfactory where there is more than a single location of interest. A further disadvantage of this type of strain gage is that it is not capable of measuring large strains, in the 5% range for example, over a large number of load cycles. Mechanical extensometers, while possessing short gage lengths, are uniaxial in operation and, due to their overall size, are difficult to use in close proximity to one another for simultaneous biaxial measurements. There is therefore a definite need in the art for a device which will measure biaxial high level strain over many load cycles, which is small in size, easily affixed to the test specimen, reusable, and eliminates the need for conversion computations to be performed on its output.
It is therefore an object of the present invention to provide a strain transducer which is capable of biaxial measurement of high level strain.
It is a further object of the present invention to provide a strain transducer which is reusable.
Another object of the present invention is to provide a strain transducer which by its relative size and weight lends itself to a variety of attachment methods.
An additional object of the present invention is to provide a strain transducer which provides output directly proportional to the strain measured, to thereby eliminate conversion computations.